1. Field of the Invention
This invention relates to technology for storage of electronic files.
2. Description of the Related Art
NAS (Network Attached Storage) provides file-sharing functions to client computers (hereafter “clients”). Communication protocols used by clients for NAS access include NFS (Network File System) and CIFS (Common Internet File System).
A file transmitted from a client is stored in a NAS file system. A file system is generally constructed in a logical volume; as such a logical volume, a logical volume created using an LVM (Logical Volume Manager) is used.
An LVM is a computer program having functions to combine a plurality of LUs (Logical Units) to create a single VG (Volume Group), and to allocate from the VG a plurality of LVs (Logical Volumes). Normally, a continuous region of size estimated in advance has been allocated as a partition and a file system has been constructed, in order to modify the storage capacity, a separate second file system is created, and data is copied from the first file system to the second file system. However, by using a LVM a single file system can be created combining a plurality of LUs, without any need to consider a continuous region, by adding LUs the file system can be expanded, and in other ways also volume management becomes more flexible.
FIG. 1 shows an example of the relation between a file system and logical volumes.
Volumes which are shaded represent elements visible from a GUI screen (for example, a screen provided to the client), and volumes with no shading represent volumes not visible in a GUI screen, but visible to CLI (for example, in a screen provided to the management terminal). In FIG. 1, the layer below the double lines represents volumes managed by the storage system 809 connected to NAS, and the layer above the double lines represents volumes managed by NAS 801.
In the storage system 809 are for example a plurality of PDEVs (physical devices) and a plurality of LUs (logical units). One PDEV is constructed from storage areas provided by one or more storage devices provided in the storage system 809. One LU is constructed from one PDEV, or from a plurality of PDEVs combined into one (for convenience called a “LUSE” or Logical Unit Size Extension”).
The NAS 801 comprises a file sharing program 803, file system (FS) program 805, and LVM 807. The LVM 807 manages, for example, SCSI devices, PVs (physical volumes), VGs (volume groups), and LVs (logical volumes). One SCSI device is one LU recognized by the NAS. The PV is created by securing a region for LVM use (VGDA (Volume Group Descriptor Array)) at the beginning of the disk image for a specific device (for example, an LU, hard disk drive, or similar). The VGDA can hold the name of the VG to which it belongs as well as information relating to all the PVs of the VG, or information relating to all allocated LVs. A VG is constructed from a plurality of PVs. An LV is a virtual device, created by allocation from a VG, and can be used similarly to an ordinary physical device. The FS 805 is constructed on an LV.
Japanese Patent Laid-open No. 2006-127143 discloses technology which merges a plurality of physical volumes to provide a single logical volume.